Check service existence before use in Debug mode

Yavsc/Controllers/Accounting/ManageController.cs

@@ -302,6 +302,9 @@ namespace Yavsc.Controllers
         public async Task<IActionResult> SetGoogleCalendar(string returnUrl, string pageToken)
 
         {
+#if Debug
+          if (_calendarManager==null) throw new Exception("No service!");
+#endif
             var calendar = await _calendarManager.GetCalendarsAsync(User.GetUserId(), pageToken);
             if (calendar == null)
               return new ChallengeResult();